Natural Weathering of Bedrock Believed to be Source of Contaminant
Arsenic concentrations that exceed current recommended federal levels for drinking water are 10 times more likely to be found in domestic wells than in municipal water sources in New Hampshire, according to a study by researchers at Dartmouth College. Arsenic in drinking water is linked to certain types of cancer in humans.
Results of the study, involving nearly 1,000 water samples, are scheduled to appear in the May 1 print issue of the peer-reviewed journal Environmental Science & Technology, published by the American Chemical Society, the world's largest scientific society. The study was initially published March 20 on the journal's web site.
The article claims that water from domestic New Hampshire wells contains "significantly more arsenic than water from municipal sources," in some cases more than three times the current maximum contaminant level (MCL) of 50 parts per billion (ppb) established by the U.S. Environmental Protection Agency.
A report issued last week by the National Academy of Sciences concluded that the current EPA standard was too high to adequately protect against the risk of cancer, and needed to be addressed "promptly."
Several clusters of elevated arsenic levels in 'bedrock' wells were found in the southeastern and south central parts of the state, mostly near the cities of Manchester and the state capital, Concord, according to the study. Domestic bedrock wells that are drilled deep into New Hampshire's underlying granite base generally have much higher arsenic levels than shallow surface wells, say the researchers.
The article cites another study published last year by the U.S. Geological Survey, involving water samples from several New England states, Massachusetts, Maine, New Hampshire, Rhode Island and Vermont, that showed ten to 15 percent of the region's domestic bedrock wells exceeded the EPA guideline.
Arsenic in water can occur naturally or as a result of its use in industrial processes, agriculture, and as a wood preservative. The bulk of the arsenic contamination of wells in the Dartmouth study appears to be due to a natural phenomenon, weathering of bedrock, rather than anthropogenic (caused by people), according to the article.
Although arsenic is found in many types of geological conditions, a coarse-grained granite derivative called pegmatite, common to many parts of New England, appears to be the most likely source for the arsenic in New Hampshire well water, the article states.
As a result of the recent NAS report, EPA is considering lowering the maximum contaminant level for arsenic in drinking water from 50 parts per billion to somewhere between two to 20 ppb, says Stephen Peters, one of the Dartmouth researchers.
However, he points out in the journal article, "While changes in the MCL will directly affect towns and cities regulated by the U.S. EPA, they have no regulatory consequences for domestic wells, which are defined as those serving less than 15 households or 25 individuals." The study concludes that tighter federal guidelines would not necessarily "alleviate the health risk" to people who get their water from domestic wells that are not regulated by EPA.
The article claims that 15 percent of the U.S. population, including nearly 40 percent of the people in New Hampshire, obtain their water from domestic wells, most of which, it says, have not been tested for arsenic.
A nonprofit organization with a membership of nearly 159,000 chemists and chemical engineers, the American Chemical Society publishes scientific journals and databases, convenes major research conferences, and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.
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